Ciat-Lonbarde Tetrazzi Organus Eurorack Modular Synth Module DIY conversion – with added CV control !

This is a photo tutorial on how to “eurofy”a tetrazzi organus. The tetrazzi organus is a touch sensitive synthesizer that generates highly banded sounds using piezo trasducers attached to rigid boards – press barres. In my implementation y shall teach you how to make the press barres CV controllable with + AND – voltages (you cannot believe how freaking good this sounds!). Additionally i suggest how to construct a euro faceplate and how to power the tetrazzi board using your onboard Doepfer style cable and power supply. This is a physical contraption that I deliberately named E.U.R.A.Z.Z.I.

Why did I do this? because the E.U.R.A.Z.Z.I. was instrumental on interpreting my 2003 graphic score composition entitled “Sonnet“. This composition is based on the juxtaposition of, (i) numerological findings and (ii) musicality features, both systematically extracted from the poem “Sonnet” by Federico Garcia Llorca:

I do not wish to distract you from your eager DIY intentions but, if you want a taste of the E.U.R.A.Z.Z.I’s capabilities you can check “Sonnet” track as follows:

Federico Garcia Lorca - Sonnet

   I know that my profile will be serene
in the north of an unreflecting sky.
Mercury of vigil, chaste mirror
to break the pulse of my style.

   For if ivy and the cool of linen
are the norm of the body I leave behind,
my profile in the sand will be the old
unblushing silence of a crocodile.

   And though my tongue of frozen doves
will never taste of flame,
only of empty broom,

   I'll be a free sign of oppressed norms
on the neck of the stiff branch
and in an ache of dahlias without end.

The tetrazzi organus is defined by Professor Blasser as follows:

“Tetrazzi is the newest incarnation of the Organus series, a mandala of analog oscillator circuits that can cross-modulate to form the empire of infinite circuitry known as pure sonic chaos. Electronically, it represents some of the more profound electronic complices that were developed in the 20th century,  such as Buchla Source of Uncertainty,  U.S. Navy Phantastron Radar Circuit, and Piezoelectric Flex Technology. It is a way to make the touch-sensitivity of human organs into touch-sensitivity on the pipe organ, pipe here meaning “squishing electron flow via ceramic transducer”.  You got to love this man!

Step 1: assemble the tetrazzi board as per Senior Blassier instructions

Step 2: I used a Doepfer A-100B42 42 HP / 213 mm blank panel as a guide to cut a wood front panel from a 3.5mm timber sheet.

Step 3: give it a bit of a sand and mark the mounting holes.

Step 4: cut another sheet of the same height but 5-6 cm narrower – this will make your press barres

Step 5: divide the 2nd sheet on 4 equally sized press barres … ca va?

Next … step: i have a jigsaw + I am sloppy so i have to sand them all down to straight sides!

then … your press barres sould look like this 

the next step: get some M3 screws/nuts and place your press barres – the nuts will serve as spacers that will elevate all barres at the same height. it is also a good idea to number all barres 1 to 4 and make sure that:

1. you drill and place the screws so that you clear the mounting rails

2. the screws can conduct electricity – they will be your bend/touch points (4/barre)

take the plunge into the next step! … give your timber tender loving care with a bit of oil or varnish … make it look gorgeous!  

what’s up now? another step: drill and mount

1. x4 momentary switches

2. 4 pots – 100K

3. L-out and R-out (middle left and right jacks)

4. x4 CV in jacks for press barre modulation

… also drill 4 holes for press-barre piezo cables to be solder into the tetrazzi board

LooKing GooD! don’t you think? –

step (n+1) … attach the tetrazzi board to the back-panel … i used PCB stick-on elevators – – you might also use brackets – crews+PCB separators … you decide my friend!

now solder all panel components to where they suppose to be according to ciat-lonbarde’s assembly instructions … i will tell you how to wire your barre-CV-in’s soon – do not despair amigo.

now, how to build and connect you Doepfer-style ribbon connector … the next image will tell you that you would solder all GND pins together and all +12 volts pins together and then just connect +12 and GND to whey belong in the tetrazzi board (the PSU adapter points)

now triple-check your doepfer jack since you now shall epoxy this baby onto the board and against one on the jack triplets. Use clamps to assist epoxy-driven union and let cure according to your epoxy instructions

voila … you have officially EUROfied a tetrazzy – since you have all that epoxy goo mix drying out, hurry and glue the piezos to the barre boards and then attach the barres to your panel – remember – one nut serve to elevate the barre from the panel and a 2nd nut shall secure it to the dorsal/back panel. do not forget to solder the piezos on the board  🙂

ahora … otro paso: give your baby its umbilical cord – she is hungry!

well, the time has come, i’ll let you know: for your barre-CV-in’s, wire GND of each CV jack (the closest jack-pin to the panel) to its corresponding black/GND piezo connection at the board. the connect each CV-jack-tip-pin to a 330K resistor and the other end of the resistor to the red/positive piezo connector at the board. if you have an eagle eye you can see this at the next couple of pics …

happy chappy ? you bet – you have build a tetrazzi organus into your eurorack modular synth. you can CV-modulate it using bipolar voltages and also play-it with your pressure gestures concomitantly

if you build one of these … please let me know and send some pics: that will pay-off the time and effort that I invested into this post. lots of love,



6 thoughts on “Ciat-Lonbarde Tetrazzi Organus Eurorack Modular Synth Module DIY conversion – with added CV control !

  1. Pingback: Sonnet | LopezDoNaDo

  2. Hi! Thanks for this guide – I just ordered a kit and will give it a try when it arrives. Do you have a photo of the finnished “module” in your eurorack case?

      • Looks nice!

        I’m nearly finnished with my eurorack conversion – but I have some questions for you.

        1. What does the CV in control? Pitch?
        I tried your method and input an LFO but it just made the barres do nothing, and no sound comes out. I have the jacks wired after your instructions – ground to piezo GND and signal pin to positive piezo.

        2. Why the 330K resistor?

        3. Have you tried any other mods mentioned in the Tetrazzi manual?

        Thanks for helping out 🙂

  3. Piezo GND is no good – I used the GND from the ribbon cable instead. I also switched out the resistors with capacitors instead for an interesting effect! Now it works!

    I also have CV in for the UPTON, DONTON, DONMOD & UPMOD + individual outs for each oscillator 🙂

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